1ShoppingCart would rule the eCommerce world if you just...

Integrate Stamps.com with 1shoppingcart.

Stamps.com is the number one online source for all of your shipping needs through the post office. It would be great if 1shoppingcart integrated with stamps.com to have all order information exchanged and all shipping tracking information exchanged back to the cart. Stamps.com works great with Amazon and ebay, why not 1shoppingcart.com too.

Go to MyShippingPartner.com and get an account. It's a fantastic webapp. that works as middleware between 1ShoppingCart and Endicia (which is a discounted US Postal Service postage company). It does exactly what you want, works great, great interface, etc.